A very nice section of SICP[1] describes how cons/car/cdr can be built only
with functions. Translated to Clojure it might look like
(defn cons [a b]
#(condp = %
:car a
:cdr b))
(defn car [cons-cell]
(cons-cell :car))
(defn cdr [cons-cell]
(cons-c
In the previous post, I accidentally deleted a dot when pasting:
user=> (clojure.lang.MapEntry :a 1)
should have been
user=> (clojure.lang.MapEntry. :a 1)
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A cons is essentially just a struct with two fields. In Clojure, it's sort
of like:
(defrecord Cons [car cdr])
(defn cons [x y] (Cons. x y))
(defn first [x] (:car x))
(defn rest [x] (:cdr x))
The amazing thing is that you can represent any collection of arbitrary
length, just by nesting these st
On Jun 16, 11:37 am, David Nolen wrote:
> Not possible in Clojure and a source of hassle in Scheme and Common Lisp.
> If you have dotted pairs you can never know if you have a proper list.
I'm probably missing some context, but I've heard this argument before
and had a hard time understanding it.
>
> I have a need to learn enough scheme to read it and write a few functions.
> I came across dotted pair notation. I am trying to grok it in terms of the
> only Lisp I know, Clojure. Does dotted pair notation in Scheme compare to
> form in Clojure, and if so, how?
>
As David notes, dotted-
dotted pairs and cons in Scheme and CL both allow you specify an improper
tail. This has some historical utility if you are using cons as a way to
build up non-list data structures. Scheme and CL both provide better
facilities for data structures than using cons.
As far as I know lists are just co
Thanks for answering. I am taking from your answer that I can be
Lisp/Clojure-esque in Scheme and not worry about dotted pairs. That is, I
can make a grid out of lists, rather than using cons to construct them.
That's what I'm trying to do.
On Saturday, June 16, 2012 11:35:14 AM UTC-4, octopusg
Not possible in Clojure and a source of hassle in Scheme and Common Lisp.
If you have dotted pairs you can never know if you have a proper list.
David
On Sat, Jun 16, 2012 at 11:35 AM, octopusgrabbus
wrote:
> I have a need to learn enough scheme to read it and write a few functions.
> I came acr
I have a need to learn enough scheme to read it and write a few functions.
I came across dotted pair notation. I am trying to grok it in terms of the
only Lisp I know, Clojure. Does dotted pair notation in Scheme compare to
form in Clojure, and if so, how?
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